Someone "just turned around and started shooting," Casseus, 40, recalled in a phone interview Tuesday, referring to an unknown shooter who killed Franklin Francois, 25, just before 2 a.m. Sunday near Sixth Avenue North and 11th Street North.

Fearing for his safety and not knowing where the shooter was headed next, Casseus fled inside his office and took cover.

"You just don't know what to think in that moment," he said. "So my best thinking is: Get my head low ... and go straight back to my office."

He called 911, and the dispatcher asked him what he could see. Casseus carefully peered out the window and saw a white shirt on the ground. The dispatcher asked Casseus whether he could tell who the person was or whether he could make it out there.

"I said, 'I'm not sure, but I really can't go out there, because I don't know where the shooter is,' " Casseus recalled.

When a police officer arrived at the scene shortly after the call, Casseus went outside and asked whether everything was OK.

"He said, 'Bring me towels, bring me towels,' " Casseus recalled.

Casseus grabbed a couple of towels from his office and raced back outside. The officer told him to help stop the bleeding as Casseus pressed the towels against Francois' stomach.

An officer attempted mouth-to-mouth resuscitation, Casseus said. It was then that he could feel Francois' heartbeat.

"His heart beat like three times: Boom. Boom. Boom," Casseus said. "It starts giving you hope that whoever that is hopefully will survive."

Then another round of cardiopulmonary and mouth-to-mouth resuscitation.

Nothing.

Francois, of Fort Myers, was taken to NCH Baker Hospital Downtown, where he was pronounced dead, Naples police said.

Since those frantic moments in Sunday's early hours, one question has stuck with Casseus: What if he had gone out to Francois sooner? Could he have survived?

"I wish I came out there sooner," he said. "If I came out there sooner, maybe it might mean another second to live, maybe that would give him that time to make it to the hospital. ... Nobody's supposed to die like this."

Casseus said the phone call from his wife that pulled him outside his office that night was an opportunity to make a difference.

"That was a signal for me to help somebody that night," he said. "And I didn't do it quick enough. I didn't feel brave enough to go out there."

Francois' family came to see him Tuesday, Casseus said. He told them about his regrets.

But they thanked him for what he did, Casseus said, and told him that "maybe it wasn't meant to be."

Casseus, who has four boys between 5 and 11 years old, said he didn't recognize Francois in the heat of the moment but later realized he had often seen him around the neighborhood. A 2009 Naples High School yearbook lists a Franklin Francois as a sophomore.

"It's painful; it's like I'm witnessing a kid dying like this," Casseus said. "All I can think of is my kids."

Casseus said he doesn't know what led to the deadly shooting.

"Nobody knows anything at all," he said.

A Naples police spokeswoman said Tuesday the investigation is active.

"Unfortunately, there are no updates and/or arrests at this point," Marie Reese wrote in an email.

According to a Naples police arrest report, a man matching a witness's description of "the individuals running from the area of the gun shots" was detained at 1300 Fifth Ave. N. shortly after shots were reported Sunday.

The man was arrested on suspicion of possession of cannabis, the report states.

When asked whether the man is considered a suspect in the shooting, Reese said in an email that "everything is being considered."

Casseus said he hopes the shooter will be caught.

"I really want to see whoever that is pay for it," he said. "That's the only way I can really heal my pain, knowing that somebody gets caught and (pays) for it."